Camshaft phasers for varying the phase relationship between the pistons and the valves of an internal combustion engine are well known. Some prior art camshaft phasers include a torsion bias spring to bias the rotor toward an extreme rotational position. Typically, such a spring is accommodated on an arbor within a well within the rotor hub. Others may reside on the outside of the stator cover around the arbor.
A torsion spring changes diameter as it is torsionally deflected. Further, in loading such a spring, moments are inherently applied to the spring which must be counteracted in the restraint of the end coils, which twisting moments also act to distort and shift the body of the spring away from the central axis of the spring and the phaser. Further, such a spring requires radial clearance in the well, typically between about 5% and about 10% of the spring rest diameter, to allow the spring to move freely.
In prior art camshaft phasers employing a torsion coil spring as just described, the twisting moments cause the spring to be distorted off-axis and the outermost coils (end coils) of the spring to engage the walls of the arbor and, when applicable, the well, thereby increasing the frictional hysteresis of the torsional spring load, resulting in excessive wear and premature failure. The resulting observed spring rate is less than intended and the resulting observed load deflection curve includes a large amount of frictional hysteresis.
What is needed is a phaser arrangement wherein the spring end coils remain centered on the phaser axis and the other coils experience little or no contact with walls of the rotor well and arbor.
It is a principal object of the present invention to increase the observed spring rate and lower the frictional hysteresis of a torsional bias spring in a camshaft phaser.